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Old 21st September 2012, 18:20   #16
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Default Re: Why the Twin-Stage Turbo & not a VGT?

In principle VGT provides low down power as well as higher up the rev range power. But this depends on how you have tuned the turbo. The previous verna was VGT but was tuned only for top end, hence the crazy pull, and mediocre bottom end.

I think mahindra did not want a VGT primarily for this purpose. Probably two old school turbos in unison work better in this application (1500 Kgs) rather than a not so fancy VGT. My views.

Last edited by Ford5 : 21st September 2012 at 18:22.
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Old 21st September 2012, 23:23   #17
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Default Re: Why the Twin-Stage Turbo & not a VGT?

1) Application. The Quanto is also likely to end up in rural, semi urban markets where relatively complex turbo idling procedure might not be followed. VGT maintenance is not possible in these operating conditions.

2) Regular maintenance and/or problem diagnosis. Again a relatively tough part with Mahindra as Mahindra is mainly a utility vehicle manufacturer, and service at smaller towns might not be able to handle more complex VGT.

3) Cost. To the best of my knowledge, two turbo would cost less than one complex VGT.

4) Again, correct me if I am wrong, but in case of VGT, you can do tuning such that you either win lower end or top end, but cant achieve linear-ness one can get with twin turbo.
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Old 22nd September 2012, 02:00   #18
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Default Re: Why the Twin-Stage Turbo & not a VGT?

Quote:
Originally Posted by groom View Post
I was discussing the launch of Quanto with one of my ex-colleague and also a friend (who is extensively working on Turbo Tech) but we could never understand why Mahindra went for twin turbo instead of VGT.

.....

As you can see, most engines have reached to 100 or over 100BHP easily by just changing the turbo technology from normal turbo to VGT.

My Friend: Normally a two stage turbo will have a turbine size of 42mm (Low Pressure) and 35mm (High Pressure), but VGT covers both the flow ranges and still able to deliver the power density.

...

The change from normal turbo to VGT is simple, not much modifications, cost less, and frugal engineering. On the other hand, twin turbo is a major modifications, even bigger for Mahindra, especially hearing how things proceed in Mahindra on the THAR threads,...

Is it two-parallel tubochargers or two-stage turbo? Mahindra website says "India's first twin-stage" but then corporate communication departments are not paragons of technical accuracy.


Also why would twin-stage turbo be more expensive than VGT? I would have thought it to be the other way round. VGT as vanes with adjustable angle of attack - that is a far more complicate system than just having two turbos one after the other.


Twin-stage turbos have been used mainly in very high power engines - first turbo adds pressure (as much as is feasible with current technology) and then the second adds more. Obviously in those applications it is very expensive.
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Old 22nd September 2012, 04:26   #19
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Default Re: Why the Twin-Stage Turbo & not a VGT?

As soon as I read that the Quanto uses a twin turbo setup, this chart flashed into my mind:


Its easy to see here which engines use Twin Turbos and which ones use VGTs.

The following lines from the new 3-Series official review also came to my mind.

Quote:
Driveability within the city is top class, and all that's required for regular commuting is a light tap on the accelerator pedal. Power delivery is linear across the rpm range
Isn't ^^^ what Renuka Kriplani said in her video review of the Quanto?



Of course the tech used might not be as advanced as that used on the BMW, it is a start and a very important stage in engine development for M&M considering the immense utility of such an engine in other M&M vehicles.

In a similar state of tune, it could help bring down the prices of a Thar mCR100 AC 4X4 down to Swift LDI levels (By saving excise duties).

It could help them stop royalty payments to Renault on something like a Verito and finally take it forward from its original 2007 form. Also help reduce prices on it and make it a more powerful and hence more desirable than what it is in its current form (the least powerful sedan in the country).

This experiment of theirs with a Twin Turbo could help them gain vital experience in making more powerful future engines for, say, the XUV7OO or a lighter + downsized + more efficient engine on the W105 (new Scorpio).

Maybe by doing this, they were looking at long term benefits and not a shortcut which would have allowed them to introduce the Quanto in the market much faster.

P.S.: At just about 2 seconds slower than a Swift VDi to a 100kph, it isn't as slow as it is made out to be. 17-18 seconds for a ton is pretty much par for most ladder frame UVs.
P.P.S: I have seen many a Quanto Test Mule barreling down NH3 at 140+ speeds. Believe me its definitely no slouch.

Last edited by antz.bin : 22nd September 2012 at 04:29.
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Old 22nd September 2012, 07:47   #20
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Default Re: Why the Twin-Stage Turbo & not a VGT?

Its a great move by Mahindra to bring this engine. I am sure we are going to see different configurations of the same engine.

I am only worried about this word 'experiment'!
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Old 22nd September 2012, 14:07   #21
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Default Re: Why the Twin-Stage Turbo & not a VGT?

I do not agree to the mathematical calculation of 0.99 x 0.99 to achieve 0.98 reliability.
The reason being a VGT is a very complicated piece of machinery especially its vane changing mechanism and its interface with electronics. Such complicated things can reduce reliability in long term more than compared to two simple Turbo's. Twin turbo might be a robust setup than the VGT.
Also I feel on the emission part the twin turbo is a better setup because I have seen larger engines using this technology more than the VGT setup.
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Old 22nd September 2012, 20:52   #22
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Default Re: Why the Twin-Stage Turbo & not a VGT?

So I was hanging out with a M&M employee today who has worked on the Quanto (and is currently working on the W105 aka the All New Scorpio). According to him, the original plan was to plonk in a VGT. But considering the heft, it had too much Turbo Lag. Also, the 3 cyl engine was so excessively vibey that the engine mounts would break, and the intercoolers would break as if they were Parle G biscuits. So the RnD dept. was busy in resolving the NVH issues til very late in the testing process. In fact, this NVH hurdle meant that the product was postponed by 1 full year. Quanto was supposed to be launched in September 2011 but could only make it on the roads in September 2012. They had benchmarked the Fabia/Polo (the competition 3-Pot Diesel cars) for this and have bettered the Quanto's NVH (inside and outside the car) in comparison.

In the meantime, in an entirely different RnD project, some other guys were experimenting with Twin Turbo Setup for the mHawk which would bump up the horsepower to 190 bhp from the same 2.2 liter block. (the mHawk is capable of 170 bhp with a slightly modified VGT and a slightly different ECU tune which these people had access to while testing).

Both projects came together as an experiment while the Quanto engine was being worked upon for NVH correction and as a result, the excess Turbo Lag problem was also solved at a lower price as compared to a VGT. This same engine was made in 2 tunes, the current 100bhp and another one with 120bhp. The Quantos with the 120bhp Twin Turbo engines would top out at around 180kmph on the speedo. But in the interest of overall safety (and maybe cost cutting) these guys used the 100bhp tune engine on production Quantos which will top out at around 155kmph.

All these top-end testing is usually done on the Mumbai-Pune Expressway where test drivers clock around 700-800km daily on test mules in 2 shifts.
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Old 29th September 2012, 18:36   #23
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Default Re: Why the Twin-Stage Turbo & not a VGT?

My understanding is that a twin stage will multiply the boost pressure more than a VGT. That's why the twin stage or two stages. The first stage multiplies the pressure upto 3 or 4 times the normal pressure (like a VGT). The second stage takes where the first stage multiplication left off (3 or 4 times the normal) and multiplies it even further upto 8 or 9 times the normal pressure. I reckon this is to overcome the inherent lack of low-end torque that's characteristic of a 3 cylinder diesel. This could be the reason for the flat torque across a RPM range in the Quanto's diesel.

Last edited by swiftdiesel : 29th September 2012 at 18:37.
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Old 2nd October 2012, 00:06   #24
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Default Re: Why the Twin-Stage Turbo & not a VGT?

Quote:
Originally Posted by hemen View Post
IMHO Mahindra had to go twin turbo due to huge weight of Quanto in comparison to others and using a 3-POT engine.
Didn't know the Quanto runs on a 3-cylinder engine. Soon as I read this, I googled it and Indiatoday link that came up quotes Mahindra saying "Quanto's 1.5 Liter, 3 cylinder diesel engine is the smallest diesel motor in the world to feature a twin turbocharger."

Quote:
Originally Posted by antz.bin View Post
As soon as I read that the Quanto uses a twin turbo setup, this chart flashed into my mind:

Let me guess, Volvo and the Merc ?
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Old 2nd October 2012, 00:57   #25
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Default Re: Why the Twin-Stage Turbo & not a VGT?

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Originally Posted by DudeWithaFiat View Post
Let me guess, Volvo and the Merc ?
Among the Diesels: the 184bhp 2 liter Bimmer and the 204bhp 2.2 liter Merc.

Don't know about the petrols but my guess is none of these come with 2 Turbos yet.
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Old 2nd October 2012, 15:13   #26
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Default Re: Why the Twin-Stage Turbo & not a VGT?

Following article provides sufficient details on this subject. With staged turbo chargers both higher power and torque are possible at low rpms.
Mitsubishi Heavy Industries Technical Review
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Old 2nd October 2012, 17:08   #27
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Default Re: Why the Twin-Stage Turbo & not a VGT?

Test drove the Quanto yesterday & I am thoroughly impressed with the way a vehicle of this size moves. I was primarily interested in getting to know the engine since I believe that it would make it to the Verito.

So, personally, the engine is a gem. Agreed that its a 3-cylinder, but as long as its quick & reliable enough (looking at the general history of Mahindra's technical expertise & the 2.2 mHawk's reputation), I have no qualms. If you look at it from another perspective, there are lesser moving parts as well since it has one full cylinder lesser than the contemporaries.

Even with a weight of more than 1.5 tons, the engine pulled the vehicle effortlessly. I couldn't go beyond 80ish but I believe that the Quanto is capable of cruising on 100 all day long. I can only imagine what this cracker of an engine would do to a sedan (like the Verito) or a hatchback.

So basically, whatever Mahindra has done with the twin-stage turbo, I feel it works. As most have said, they have built a basic yet powerful "big" car that does not use many fancy parts.

Last edited by blackfire_9 : 2nd October 2012 at 17:11.
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Old 18th December 2012, 12:38   #28
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Default Re: Why the Twin-Stage Turbo & not a VGT?

Quote:
Originally Posted by antz.bin View Post
Also, the 3 cyl engine was so excessively vibey that the engine mounts would break, and the intercoolers would break as if they were Parle G biscuits.
So does it mean the twin turbo resolves out/reduces the engine vibrations to a certain extent? If yes, in what way?
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Old 19th December 2012, 22:27   #29
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Default Re: Why the Twin-Stage Turbo & not a VGT?

Post # 22 is correct IMO.

Project A got mixed with Project B - Lateral Thinking and wow - We have the QUANTO!
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